MEF2C repressor variant deregulation leads to cell cycle re-entry and development of heart failure.

BACKGROUND: A pathophysiological link exists between dysregulation of MEF2C transcription factors and heart failure (HF), but the underlying mechanisms remain elusive. Alternative splicing of MEF2C exons α, ß and γ provides transcript diversity with gene activation or repression functionalities. METHODS: Neonatal and adult rat ventricular myocytes were used to overexpress MEF2C splicing variants γ+ (repressor) or γ-, or the inactive MEF2Cγ+23/24 (K23T/R24L). Phenotypic alterations in cardiomyocytes were determined by confocal and electron microscopy, flow cytometry and DNA microarray. We used transgenic mice with cardiac-specific overexpression of MEF2Cγ+ or MEF2Cγ- to explore the impact of MEF2C variants in cardiac phenotype. Samples of non-infarcted areas of the left ventricle from patients and mouse model of myocardial infarction were used to detect the expression of MEF2Cγ+ in failing hearts. FINDINGS: We demonstrate a previously unrealized upregulation of the transrepressor MEF2Cγ+ isoform in human and mouse failing hearts. We show that adenovirus-mediated overexpression of MEF2Cγ+ downregulates multiple MEF2-target genes, and drives incomplete cell-cycle reentry, partial dedifferentiation and apoptosis in the neonatal and adult rat. None of these changes was observed in cardiomyocytes overexpressing MEF2Cγ-. Transgenic mice overexpressing MEF2Cγ+, but not the MEF2Cγ-, developed dilated cardiomyopathy, correlated to cell-cycle reentry and apoptosis of cardiomyocytes. INTERPRETATION: Our results provide a mechanistic link between MEF2Cγ+ and deleterious abnormalities in cardiomyocytes, supporting the notion that splicing dysregulation in MEF2C towards the selection of the MEF2Cγ+ variant contributes to the pathogenesis of HF by promoting cardiomyocyte dropout. FUNDING: São Paulo Research Foundation (FAPESP); Brazilian National Research Council (CNPq).

Increased expression and phosphorylation of focal adhesion kinase correlates with dysfunction in the volume-overloaded human heart.

FAK (focal adhesion kinase) has been shown to mediate the hypertrophic growth of the left ventricle. Experimental results also suggest that FAK may contribute to the structural and functional deterioration of the chronically overloaded left ventricle. In the present study, we postulated that FAK expression and phosphorylation may be altered in the volume-overloaded heart in humans. FAK expression and phosphorylation at Tyr(397) were detected by Western blotting and immunohistochemistry in samples from endomyocardial biopsies from patients with MR (mitral regurgitation; n=21) and donor subjects (n=4). Hearts from patients with MR had degenerated cardiac myocytes and areas of fibrosis. In this group, the myocardial collagen area was increased (18% in MR hearts compared with 3% in donor hearts respectively) and correlated negatively with left ventricular ejection fraction (r=-0.74; P>0.001). FAK expression and phosphorylation at Tyr(397) (a marker of the enzyme activity) were increased in samples from MR hearts compared with those from donor hearts (3.1- and 4.9-fold respectively). In myocardial samples from donor hearts, anti-FAK staining was almost exclusively restricted to cardiac myocytes; however, in myocardial samples from MR hearts, staining with the anti-FAK antibody was found to occur in myocytes and the interstitium. There was a positive correlation between collagen and the interstitial areas stained with the anti-FAK antibody (r=0.76; P>0.001). Anti-FAK and anti-vimentin staining of the interstitial areas of samples from MR hearts were extensively superimposed, indicating that most of the interstitial FAK was located in fibroblasts. In conclusion, FAK expression and phosphorylation are increased and may contribute to the underlying structural and functional abnormalities in the volume-overloaded heart in humans.

Left ventricular reconstruction brings benefit for patients with ischemic cardiomyopathy.

BACKGROUND: Optimal treatment strategies for some patients with ischemic cardiomyopathy can be unclear. We compared the outcome for patients treated with revascularization only or with additional ventricular reconstruction. METHODS AND RESULTS: We compared 74 consecutive patients with an ejection fraction <35% and a left end-systolic volume index >80 mL/m(2). All patients underwent revasularization but some received only revascularization (group 1) and some were randomized into a group that received additional ventricular reconstruction (group 2). Preoperative and postoperative ejection fraction, end-systolic volume, mitral regurgitation, mortality, heart failure (HF) symptoms, and recurrence were compared between groups. There was 1 postoperative death in group 2 (P =. 58). Preoperative ejection fraction between the groups was similar (P =. 19) but it differed significantly postoperatively (P < .001). HF class (New York Heart Association) decreased more in group 2 (group 2, 2.3 +/- 0.4 versus group 1, 1.4 +/- 0.4; P < .001). Incidence of HF recurrence and rehospitalization was significantly less in group 2 (P = .028). The postoperative development of higher-grade mitral regurgitation was greater in group 1 (147 +/- 32 mL/m(2) versus 119 +/- 25 mL/m(2), P = .024). CONCLUSION: The outcome at midterm of coronary artery surgery alone in patients with a preoperative large left ventricle was inferior compared with the outcome achieved with additional ventricular restoration.

Left ventricular reconstruction benefits patients with ischemic cardiomyopathy and non-viable myocardium.

OBJECTIVE: There are subsets of patients with ischemic cardiomyopathy for whom the optimal treatment strategies are not clear. The objective of this study was to delineate the relationship between clinical outcomes and surgical procedure in patients who were treated either with a coronary artery bypass graft or with a coronary artery bypass graft and additional ventricular restoration. METHODS: The study population comprised 137 consecutive patients with anterior myocardial infarction. All patients had an ejection fraction <50% and left ventricle end-systolic volume index >80 ml/m(2). The patients were divided into a viable and a non-viable group according to anterior myocardium viability, which was determined by a thallium-201 test. The viable group underwent a revascularization and was randomized into two groups for additional ventricular reconstruction. Group 1a comprised 35 patients with viable anterior wall who underwent surgical revascularization. Group 1b comprised 39 patients with viable anterior wall who underwent surgical revascularization and ventricular restoration. Group 2 comprised 69 patients with non-viable anterior wall who underwent revascularization and ventricular reconstruction. The preoperative and postoperative ejection fractions, end-systolic volume, mitral regurgitation, mortality, and heart failure symptoms were compared among groups. RESULTS: Complete 2-year follow-up was achieved in 127 (92.7%) patients. Ejection fraction improved in all groups compared with preoperative values and it was greater in group 1b than in group 1a (p<0.001) at 2 years. There were no postoperative deaths in group 1a, one in group 1b, and two in group 2. After 2 years, group 1b was significantly smaller than group 1a (p<0.01) in relation to mitral regurgitation of grades 1 to 2+. End-systolic volume was significantly smaller in group 1b than in group 1a (p<0.001), it was smaller in group 1a than in group 2 (p<0.001), and it was smaller in group 1b than in group 2 (p<0.001). Heart failure class (NYHA) was reduced in all groups and events were significantly smaller in patients with end-systolic volume lesser than 120 ml/m(2) (p<0.05). CONCLUSION: We have demonstrated that the short-term and mid-term outcomes of coronary artery surgery alone in patients with a large left ventricle are inferior to coronary artery surgery plus ventricular restoration.